Chokes or reactors

ABSTRACT

A choke or reactor has laminations which define a U-shaped structure having two outer limbs and a base. Further laminations define a central limb connected at one end to the base and surrounded by a winding. In some embodiments the free ends of the outer limbs and the central limb are connected by laminations disposed between them. The central limb, at the said one end, may be separated from the base by an air gap.

United States Patent 1191 Koh [ 1 CHOKES OR REACTORS [76] Inventor: Chew Seng Koh, 108 J00 Chiat Terrace, Singapore, Singapore 15 22 Filed: Aug,4, 1972 21 Appl. No.2 278,125

Great Britain {336/83 1 June 4, 1974 1,166,835 Great Britain 336/212 1,489,983 5/1969 Germany 336/212 1,488,153 3/1969 Germany 1 1 336/83 446,516 3/1968 Switzerland 336/212 1,233,418 10/1960 France 336/212 Primary Examiner-Thomas J Kozma Attorney, Agent, or FirmHolman & Stern [57] 7 ABSTRACT A choke or reactor has laminations which define a U- shaped structure having two outer limbs and a base. Further laminations define a central limb connected at one end to the base and surrounded by a winding. 1n some embodiments the free ends of the outer limbs and the central limb are connected by laminations disposed between them. The central limb, at the said one end, may be separated from the base by an air gap.

11 Claims, 14 Drawing Figures PATENT-Emu 4 I914 sum 20F 4 FlG.2b.

PATENTEDJUN 4mm 3815x367 SHEET HOE 4 1 CHOKES R REACTORS BACKGROUND OF THE INVENTION This invention relates to chokes or reactors.

One known type of choke or reactor comprises a core as shown in FIGS. la, lb, or 1c. The type of choke or reactor shown in FIG. la has two stacks of E-shaped laminations with corresponding limbs of the laminations end to end. A winding is wound around the central core formed by the central limbs of the two stacks of E-shaped laminations. In the construction shown in FIG. lb, two stacks of U-shaped laminations are placed with their limbs end to end and a winding is fitted around one or both of the limbs of the thereby completed magnetic circuit. The constructions shown in FIGS. la and lb have the disadvantage that they require different blanking tools and dies for cutting laminations for different shapes and sizes of cores. A certain proportion of material has to be wasted in cutting the laminations using the blanking process.

A choke or reactor is constructed using the stacks of laminations illustrated in FIG. using the following method. A coil is wound around a central limb which consists of a stack of flat laminations and then the arms of the two stacks of U-shaped cores are fitted around the coil so as to enclose it. The limbs of the U-shaped laminations are longer than the central core so that an air gap is left at each end of the central core. The U- shaped laminations are then inserted in a tightly fitting casing and force is applied to the bases of the U-shaped laminations to push them together so as to adjust the air grip. This construction has the disadvantage that the various components have to be made to considerable accuracy as they have to fit together tightly so as to avoid vibration. This is, in practice, difficult to achieve owing to tolerances in the materials, winding techniques of the coils and the forming of the core limbs. Secondly, force has to be applied to the bases of the stacks of theU-shaped laminations to adjust the air gaps in the core and this force sometimes results in the core laminations being forced out of position and this is not easily noticeable from outside. This may cause noise and vibrationto be produced during testing and use and the only way to correct thisis to dismantle the entire choke or reactor and re-assemble it.,lt will be appreciated thatthis is expensive and it slows production.

SUMMARY OF THE INVENTION It is an object of this invention to provide a choke or reactor in which at least one of the stated disadvantages is alleviated.

According to this invention, there is provided a choke or reactor comprising laminations which define a U-shaped structure having two outer limbs, and a base, and further laminations which define a central limb magnetically coupled at one end to the said base. the free ends of the outer limbs and the central limb being connected by laminations disposed therebetween.

Suitably the two outer limbs are part of a stack of U- shaped laminations, and the central limb is provided by a separate stack of laminations which is separated, at the said one end, from the base of the U-shaped laminations by an air gap.

Alternatively each outer limb is the longer limb of a stack of L-shaped laminations, the shorter limb of one stack resting against the shorter limb of the other stack to provide a generally U-shaped structure, the central limb being provided by a separate stack of laminations which is separated, at the said one end, from the base of the U" by an air gap.

Preferably during manufacture, the width of the air gap is adjusted to set the value of the choke or reactor.

Preferably the air gap is filled with compressible material.

Preferably there is provided a casing in which the outer limbs are a close fit.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of this invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

FIGS. la, lb and 1c illustrate known chokes or reactors and have been referred to;

FIGS. 20, 2b and 2c illustrate a choke or reactor in accordance with this invention atvarious stages in its construction, and

FIGS. 3a, b, c, d, e, f, g, and h illustrate various embodiments of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 2a, 2b and 2c a casing l is filled with a quantity of resin 2 and a stack 3 of U-shaped laminations 3 is placed over the mouthof the casing l, and insulation-pad 4 being disposed at the base of the stack of U-shaped laminations 3. As shown in FIG. 2b, a central limb, comprising a stack of flat laminations 5 and having a coil 6 wound around it, is placed within the stack of U-shaped laminations 3 so as to rest against the insulation pad 4 and then short horizontal laminations 7 are inserted between the central stack of laminations 5 and the outer limbs of the stack of U-shaped laminations 3. This assembly is then pushed into the casing 1 until the stack of laminations 3 has entered the resin 2 at the base of the casing 1. If the outer limbs of the stack of laminations 3 do not fit firmly inside the casing 1 padding is inserted when the stack of laminations 3 is inserted into the casing l. The choke or reactor is then connected to a reference circuit and the assembly of the stacks of laminations 3, 5 and 7 and the winding 6 is further forced into the casing l by a force applied to the central stack of laminations 5. During this process, the insulation pad 4 is compressed so as to vary the air gap through it until the value of the choke or reactor is that desired. It will be appreciated that while the entire assembly is forced inside the casing l, the resin 2 flows up the side of the casing 1 and eventually covers the top of the assembly as illustrated in FIG.

Thevconstruction shown in FIGS. 2a, 2b and 2c has the advantages that it is not'necessary to use different tool sizes for different core shapes and sizes and only simple shearing and bending tools are necessary. Furthermore, there is little waste material and as shearing does not induce heavy stresses in the material, annealling of the laminations to relieve the stresses is not normally required. As has already been explained it is possible to use padding if the laminations 3 do not fit perfectly within the casing l and consequently as compared to the known construction shown in FIG. 10 it is not necessary for every part of the reactor or choke to be precision made. It is, in fact, possible touse padding between the limbs of the laminations 3 and the central laminations 5 should the winding 6 not wholly fill this space. Furthermore, the resin 2 fills up all the remaining space and thereby limits the vibrations.

A further advantage is that the various steps of assembly of the choke or reactor including the adjustment of its air gap, testing of the choke or reactor and sealing are all carried out in one continuous operation. Consequently, less time is required in manufacture as compared to the manufacture of the chokes or reactors shown in FIGS. la to 10 and accurate adjustments are easier to achieve.

The laminations of each stack can be secured together by bending over the outer laminations but preferably by glueing, welding, bolting, clamping or any other convenient method.

FIGS. 3a and 3b show alternative methods of inserting laminations 7 to complete the core and the FIGS. 3c to 3g show the different constructions of the outer core which can be employed.

In the embodiment shown in FIG. 3a, the laminations 7 are horizontal as in the embodiments of FIGS. 2a, 2b and 2c in contrast to the limbs of the stack of laminations 3 which have vertical laminations. In the embodiment shown in FIG. 3b, the laminations 7 are short laminations in line with the outer limbs of the laminations 3 and, as shown, are vertical. The construction of the magnetic core shown in FIG. 3c is as in the embodiments of FIGS. 2a, 2b, 20. I

In the embodiment shown in FIG. 3d, two stacks of laminations 3a and 3b are juxtaposed so that the adjacent limbs of the stacks of laminations 3a and 3b provide the central core and the remote outer limbs of the stacks of laminations 3a and 3b provide the outer limbs.

In the emodiment shown in FIG. 3e, the stacks of U- shaped laminationsS are replaced by two stacks of L- shaped laminations l and 11, the shorter limb of the stack 10 being placed on the shorter limb of the stack 11 to provide the U-shaped core.

In the embodiment shown in FIG. 3f,'two crossed stacks of U-shaped laminations l2 and 13 are provided to entirely enclose the central stack of laminations 5.

In the embodiment shown in FIG. 3g, the stack of U- shaped laminations 3 is replaced by several stacks of narrow laminations which are in'line to provide effectively a wide U-shaped core in order to reduce eddy current loss if this be necessary.

In the embodiment shown in FIG. 3h the central stack of laminations is'divided into two stacks a and 5b with a gap 14 between them. The gap 14 serves to increase the gap leakage where this is required.

In a modification of the embodiments of FIGS. 30 to 311, the laminations 7 are entirely omitted.

A choke or a reactor is the commonly used name of an inductor.

I claim:

tral limb is divided into two parts with a further air gap I. An inductor comprising laminations which define a U-shaped structure having two outer limbs with free ends, and a base, and which are bent at the junction of each outer limb and the base, further lam-inations which define a central limb, one end of which is adjacent to said base, and a winding which surrounds the central limb, the space between the central limb and the outer limbs containing no magnetic material other than at the free ends of the outer limbs, the free ends of the outer limbs and the central limb being connected by other laminations disposed 'therebetween, there being no magnetic material providing a magnetic path between the free ends of the outer limbs and the central limb other than said other laminations and the limbs and base.

2. An inductor as claimed in claim 1 wherein the two outer limbs are part of a stack of U-shaped laminations, and the central limb is provided by a separate stack of laminations which is separated, at the said one end, from the base of the U-shaped laminations by an air gap.

3. An inductor as claimed in claim 2, which comprises a plurality of stacks of U-shaped laminations disposed side by side so that their limbs and bases are in line.

4. An inductor as claimed in claim 2 which comprises first and second stacks of U-shaped laminations with the base of the first stack resting against the base of the second stack, the limbs of the stacks extending away from the respective bases-in the said direction with the limbs of the first stack in planes normal to those of the second stack, the air gap being between the said one end of the central limb and the base of the first stack.

5. An inductor as claimed in claim I wherein each outer limb is the longer limb of a stack of L-shaped laminations, the shorter limb of one stack resting against the shorter limb of the other stack to provide a generally U-shaped structure, the central limb being provided by a separate stack of laminations which is separated, at the said one end, from the base of the U" by an air gap.

6. An inductor as claimed in claim 2 wherein the air gap is filled with compressible material.

7. An inductor as claimed in claim 2 wherein the cenbetween the two parts.

8. An inductor as claimed in claim 1 wherein the laminations which connect the said free ends of the outer limbs and the central limb are normal to the laminations of the limbs. 1

9 An inductor as claimed in claim 1 which comprises a casing in which the outer limbs are a close fit.

10. An inductor as claimed in claim 9 wherein padding is disposed between the outer limbs and the casmg.

11. An inductor as claimed in claim 9 which comprises resin which covers the limbs in the casing. 

1. An inductor comprising laminations which define a U-shaped structure having two outer limbs with free ends, and a base, and which are bent at the junction of each outer limb and the base, further laminations which define a central limb, one end of which is adjacent to said base, and a winding which surrounds the central limb, the space between the central limb and the outer limbs containing no magnetic material other than at the free ends of the outer limbs, the free ends of the outer limbs and the central limb being connected by other laminations disposed therebetween, there being no magnetic material providing a magnetic path between the free ends of the outer limbs and the central limb other than said other laminations and the limbs and base.
 2. An inductor as claimed in claim 1 wherein the two outer limbs are part of a stack of U-shaped laminations, and the central limb is provided by a separate stack of laminations which is separated, at the said one end, from the base of the U-shaped laminations by an air gap.
 3. An inductor as claimed in claim 2, which comprises a plurality of stacks of U-shaped laminations disposed side by side so that their limbs and bases are iN line.
 4. An inductor as claimed in claim 2 which comprises first and second stacks of U-shaped laminations with the base of the first stack resting against the base of the second stack, the limbs of the stacks extending away from the respective bases in the said direction with the limbs of the first stack in planes normal to those of the second stack, the air gap being between the said one end of the central limb and the base of the first stack.
 5. An inductor as claimed in claim 1 wherein each outer limb is the longer limb of a stack of L-shaped laminations, the shorter limb of one stack resting against the shorter limb of the other stack to provide a generally U-shaped structure, the central limb being provided by a separate stack of laminations which is separated, at the said one end, from the base of the ''''U'''' by an air gap.
 6. An inductor as claimed in claim 2 wherein the air gap is filled with compressible material.
 7. An inductor as claimed in claim 2 wherein the central limb is divided into two parts with a further air gap between the two parts.
 8. An inductor as claimed in claim 1 wherein the laminations which connect the said free ends of the outer limbs and the central limb are normal to the laminations of the limbs. 9 An inductor as claimed in claim 1 which comprises a casing in which the outer limbs are a close fit.
 10. An inductor as claimed in claim 9 wherein padding is disposed between the outer limbs and the casing.
 11. An inductor as claimed in claim 9 which comprises resin which covers the limbs in the casing. 